Consider a Solution Made by Mixing 500

Consider a solution made by mixing 500.0 mL of 4.0 M NH₃ and 500.0 mL of 0.40 M AgNO₃. Ag⁺ reacts with NH₃ to form AgNH₃⁺ and Ag(NH₃) ₂⁺: The concentration of Ag⁺ at equilibrium is

A) 2.0 M.
B) 4.5 * 10^-9 M.
C) 1.2 *10^-8 M.
D) 1.6 M.
E) none of these